NiceHash, a website which offers Bitcoin in exchanges customer’s computing power to mine other cryptocurrencies, confirmed the security breach early today morning.

Head of marketing Andrej P Škraba told media that the hack was “a highly professional attack with sophisticated social engineering” and that about 4,700 Bitcoins, worth about $70m (£52m) were lost. “Clearly, this is a matter of deep concern and we are working hard to rectify the matter in the coming days,” NiceHash said on Facebook.

The hack has put a spotlight on the security of bitcoins.Bitcoin has no central bank or regulatory authority backing it up. The digital coins are stored in a digital wallet or on the cloud and can be used in transactions.